Answer
$490^{\circ}C$
Work Step by Step
The maximum efficiency (Carnot efficiency) is given by equation 15–5. Make sure to measure temperatures in kelvins.
$$e_{ideal}=0.34=1-\frac{T_L}{T_H}=1-\frac{(230+273)K}{T_H}$$
Solve for $T_H=\frac{T_L}{1-e}=762K\approx490^{\circ}C$.
